1. Field of the Invention
The present invention relates to clutch controls for automatically controlling the engagement and disengagement of transmission master clutches and in particular relates to clutch controls for master clutches utilized with automatic mechanical transmission systems. More particularly, the present invention relates to an improved automatic clutch control system having a modulated engagement mode wherein the master friction clutch is moved rapidly from the fully disengaged position to the position of almost incipient, or about incipient, engagement and then fully engaged in a modulated manner and wherein the position of almost incipient or incipient engagement is determined by the value of a monitored clutch actuator parameter, which value is periodically updated by monitoring the changes in value of other system parameters such as engine speed and/or input shaft speed during clutch engagement operations.
2. Description of the Prior Art
Automatic mechanical transmission systems and the automatic controls for the master clutches thereof are known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,478,851; 3,752,284; 4,019,614; 4,038,889; 4,081,065, 4,361,061 and 4,401,200, the disclosures of which are hereby incorporated by reference.
Briefly, in such automatic mechanical transmissions systems, various drive line operations include the supply of fuel to the engine, the engagement and disengagement of the master friction clutch, the shifting of the transmission and the operation of other devices such as input or output shaft brakes are automatically controlled by a control system, including a central processing unit, based upon certain measured, sensed, stored and/or calculated input parameters. Typically, the input parameters include engine speed, throttle position, transmission input and/or output shaft speed, vehicle speed, current engaged gear ratio, application of the brakes, condition of the clutch actuator and the like. The term throttle position is utilized to signify the position or setting of any operator controlled device for controlling the supply of fuel to an engine.
Referring specifically to the automatic clutch control, in a vehicle equipped with an automatic mechanical transmission, during normal operation, when starting from at rest or operating at a very low speed, the master friction clutch is modulated between fully disengaged and fully engaged conditions, i.e. is partially engaged, according to certain input parameters, to maintain the engine speed at a set value above idle speed and/or to achieve smooth starts. Typically, the set engine speed value is throttle position modulated to provide appropriate starting torque and the clutch is moved toward engagement and disengagement, respectively, as the engine speed increases above and falls below, respectively, the set engine speed value.
In another system, see above mentioned U.S. Pat. No. 4,081,065, the clutch is modulated in accordance with throttle position, engine speed and engine acceleration.
While the above automatic mechanical transmission systems are considered to be highly advantageous, they are not totally satisfactory as, in a modulated engagement mode, such as during a start from stop operation, the engagement of the clutch was modulated for its entire travel from fully disengaged to fully engaged condition rather than moving quickly to almost the incipient engaged condition and then modulating to full engagement and/or did not periodically measure and update the incipient engagement point to adjust for wear, out of adjustment conditions and the like and/or sensed the occurence of actual incipient engagement and thus could not cease rapid engagement until some period of time after incipient engagement occured. The term "incipient engagement" of the master clutch refers to the clutch condition wherein the friction surfaces are almost or just at the point of contact.
Movement of the clutch actuators from the fully disengaged to the incipient engagement position in any manner other than the fastest possible manner is undesireable as control of the system, i.e. control of engine and/or input shaft speed, by varying amount of clutch engagement (i.e. slip) is not possible during this portion of actuator movement and delays in achieving at least incipient engagement make closed loop control of the system more difficult. This is especially true as movement from the fully disengaged condition to incipient engagement may require up to about fifty percent (50%) of the total actuator disengagement and up to about thirty five percent (35%) of the full actuator supply pressure.
Failure to periodically monitor and update the point of incipient engagement, as determined by a monitored clutch actuator parameter such as actuator pressure and/or a lever position, is undesireable as wear of the friction surfaces and/or mechanical actuator members, misadjustments of the mechanical members, and the like, can cause a relatively large variance of the value of the actuator parameter corresponding to incipient engagement. By way of example only, in a typical automatic transmission system utilizing a fluid pressure applied, spring released clutch actuator mechanism, about 60 psig actuator pressure is required to fully engage the clutch and about 25 psig actuator pressure is required to reach the point of incipient engagement. It has been found that the pressure to reach incipient engagement may vary by as much as 5-6 psig during operation of the system before manual adjustment of the clutch is required.
An automatic clutch control system including means to move the controlled friction clutch from the fully disengaged condition towards the fully engaged condition as rapidly as possible, until sensing actual initial engagement of the clutch friction linings, is disclosed in above-mentioned U.S. Pat. No. 4,401,200. While this prior art system is an improvement over the previously existing systems, this system is not totally satisfactory as actual initial clutch engagement must occur and be sensed to initiate a change from the most rapid to a modulated engagement mode of operation and thus, due to sensing and change in mode of operation delays, the rapid clutch engagement is not limited to the free travel take-up only. Also a value of a monitored clutch actuator parameter, such as actuator pressure and/or lever position, corresponding to expected initial or incipient engagement is not set. Such a value, in addition to permitting most rapid clutch engagement to occur only until just prior to expected incipient engagement, provides a parameter which can be updated and compared to previously determined values to sense system damage and/or operating errors.